We use the constituent-quark model to predict the electron spectra in semileptonic meson decays. Particular attention is paid to the end-point region of the spectrum in B decays, which is important to the determination of the b→u weak mixing angle.

Recently observed $e^{+}$ kinetic-energy peaks at 336±40 keV in several heavy-ion systems have suggested the existence of a particle φ decaying to $e^{+}$$e^{\mathrm{-}}$. We construct a simple model of φ production by the electromagnetic field of the ions. It is not possible to produce φ at rest as the data require. If $m_{\phi }$ is just above 2$m_e$, then a sharp peak in the $e^{+}$ kinetic energy can be obtained if the φ velocity is sharply peaked and nonzero. Our model suggests a mechanism for this via the formation of a resonance in the ionic system for which there is independent evidence.

A complex Langevin method proposed previously is applied to the massive lattice Schwinger model. The coupled system is consistently treated by the complex Langevin equations.

There is evidence that the highest-spin states observed in nuclei are basically rotational, but that each state emits a distribution of γ-ray energies rather than a single energy. We have measured the width of this distribution and the fraction of the population that emits it, for several (unresolved) γ-ray energy regions in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}$. These widths may be related to a damping of the rotational states at the high level densities through which these cascades flow.

We measured the mass and kinetic-energy partitioning in the spontaneous fission of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$, ${}_{}{}^{259}{}_{}{}^{}\mathrm{Md}$, ${}_{}{}^{260}{}_{}{}^{}\mathrm{Md}$, ${}_{}{}^{258}{}_{}{}^{}\mathrm{No}$, and ${}_{}{}^{260}{}_{}{}^{}]$. All fissioned with mass distributions that were symmetric. Total-kinetic-energy distributions peaked near either 200 or 235 MeV. Surprisingly, these energy distributions were skewed upward or downward from the peak in each case, except for ${}_{}{}^{260}{}_{}{}^{}]$, indicating a composite of two energy distributions. We interpret this as a mixture of liquid-drop-like and fragment-shell directed symmetric fission, although theory had not anticipated this phenomenon.

The asymptotic normalization constants $C_2$ and $C_0$ for ${}_{}{}^3{}_{}{}^{}$H→n+d are calculated by the 34-channel triton wave functions obtained for the Argonne, the Paris, and the de Tourreil–Rouben–Spring two-nucleon potentials with the Tucson-Melbourne three-nucleon potential. These two-nucleon potentials without the three-nucleon potential yield the ratio $C_2$/$C_0$ at most of 0.04. The Tucson-Melbourne potential makes the value of $C_2$/$C_0$ increase about 10%. This ratio is linearly correlated with the triton binding energy without regard to the potential, provided that the potentials have the same asymptotic (one-pion exchange) behavior. From this relationship, we deduce the value of $C_2$/$C_0$ to be 0.0432±0.0015.

We present results of classical-trajectory Monte Carlo calculations for bare ions on helium atoms. We impose the Heisenberg uncertainty principle on the classical system and obtain two important benefits. Firstly, the classical He atom is stabilized and thus full four-body classical-trajectory Monte Carlo calculations are possible. Secondly, this excludes from the classical phase space those regions where electron binding energies are below the quantum mechanical ground state. As a result, the range of agreement between calculations and experiment is increased considerably towards higher energies.

The Feshbach projection-operator formalism is used to derive the asymptotic effective interaction potential between two atoms. Beyond the usual van der Waals potential, falling like ${\mathrm{x}}^{\mathrm{-}6}$, three ${\mathrm{x}}^{\mathrm{-}8}$ terms are also obtained: an attractive dipole-quadrupole term (absent in the positronium-positronium case because of symmetry), a repulsive energy-dependent term, and a repulsive mass-dependent but energy-independent one. This last term was not obtained by Manson and Ritchie using an independent method.

High-resolution spectra of new Rydberg states of ${\mathrm{H}}_2$ in the extreme uv region were obtained by two-step doubly resonant excitation followed by ${\mathrm{H}}^{\mathrm{-}}$-ion detection. Resolved Fano-line profiles showing a sign reversal of the profile index along the Rydberg series were observed for the first time in ${\mathrm{H}}_2$. Dynamical information such as lifetimes and relative transition strengths was also derived.

We report measurements of the Stark amplitude coefficients α,β for the transition 6$P_{1/2}$→7$P_{1/2}$ (293 nm) in ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$ in an external electric field E. α is determined by measurement of absorption of 293-nm light at the F=1→F=1 resonance in a cell with known electric field and interaction length, and calibrated density. β is determined from the ratio ${\beta }^2$/${\alpha }^2$ of intensities of F=0→F=1 and F=0→F=0 lines in fluorescence. We obtain α=(1.31±0.06)×${10}^{\mathrm{-}5}$${\mu }_0$ cm/V, β=(1.09±0.05)×${10}^{\mathrm{-}5}$${\mu }_0$ cm/V (where ${\mu }_0$ is the electron Bohr magneton). These results indicate substantial shielding by core electrons. β is combined with previous measurements of Im(${\mathrm{scrE}}^P$/β), where ${\mathrm{scrE}}_P$ is the parity-nonconserving electric dipole amplitude, to yield ${\mathrm{scrE}}_P$. .AE

We show that fractal viscous fingers can be formed in a Hele-Shaw cell with radial symmetry, thereby permitting their study—for the first time—without the complicating effects of boundary conditions such as those present in the conventional linear cell. We find—for a wide range of shear-thinning fluids, flow rates, and plate separations—that radial viscous fingers have a fractal dimension ${\mathrm{d}}_{\mathrm{f}}$=1.70±0.05, the same as diffusion-limited aggregation. We also quantitatively measure the set of growth sites and compare with diffusion-limited aggregation.

The nonthermal electron velocity distribution of lower-hybrid-rf–heated plasmas in the Alcator C tokamak is deduced from measurements of electron cyclotron emission with a specialized vertical viewing optics arrangement. At a density of n${¯}_e$=0.7×${10}^{20}$ ${\mathrm{m}}^{\mathrm{-}3}$, the reconstructed distribution function in the range 50 keV≤E≤230 keV shows enhancement in the parallel direction with a perpendicular spread equivalent to $T_{\perp }$≊30 keV. The line-average energetic electron density in this energy range is approximately ${10}^{17}$ ${\mathrm{m}}^{\mathrm{-}3}$ during the rf.

Pinched electron beams emit high-power microwaves by formation of a virtual cathode. Radiation occurs simultaneously with pinching or slightly thereafter. Observations of strong electrostatic fields and the partitioning of current into reflexing and transmitting populations at the same time that microwaves are emitted indicate virtual-cathode formation. Microwaves originate mainly from the virtual-cathode side of the anode. Addition of an axial magnetic field suppresses microwave radiation by inhibition of pinching.

The first direct spectral observation of critical incoherent quasielastic neutron scattering is reported. This result has been obtained by a combination of time-of-flight and high-resolution backscattering spectrometers with use of a single crystal of selectively deuterated p-terphenyl in the vicinity of the order-disorder phase transition. The relation of the incoherent-scattering results to critical coherent neutron scattering is discussed.

Discretized path-integral computations of the energy and radial distribution function of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in good accord with experiment are presented for temperatures down to 1 K at saturated vapor pressure. Results for the single-particle density matrix, momentum distribution, and condensate fraction agree at the lowest temperature with previous ground-state calculations.

The interface between a silicon (111) surface and an amorphous silicon layer deposited at room temperature is shown to retain the (7×7) periodicity of the substrate surface. Transmission electron microscopy shows the reconstructed, buried interface both by diffraction and by imaging at high resolution in plan-view and cross-section geometries. The interface reconstruction appears to differ from the surface Si reconstruction mainly by the absence of an ordered array of adatoms. If the amorphous-crystalline interface is moved nominally 15 Å by solid-phase regrowth, the 7×7 periodicity is removed. The resultant amorphous-crystal interface is exceptionally flat and shows a 1×1 diffraction pattern. The (100) 2×1 reconstruction is not preserved after amorphous Si deposition.

A numerical solution of the Ginzburg-Landau equations for superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ vortices gives the following results: The low-pressure vortex is a new ‘‘double core vortex’’ whose rotational symmetry around the vortex axis is broken. The high-pressure vortex is the v vortex. The theory gives a transition between these vortices which is in excellent agreement with experiments.

This paper reports the discovery of a new breaking of symmetry of the quantized vortex lines in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$: Vortices with broken axisymmetry are found energetically more favorable than any of the axisymmetric ones in the weak-coupling limit. Based on our extensive numerical minimization of the vortex free-energy functional, we identify the vortices occurring in rotating ${}_{}{}^3{}_{}{}^{}\mathit{B}$ at low pressures as v vortices having—in addition to broken space parity P—also broken axisymmetry Q with the nonaxisymmetry quantum number ‖Q‖=2, and with superfluid core in the axiplanar state.

We have, for the first time, measured by electron-stimulated desorption the angular distribution of electronically excited (metastable) species from CO adsorbed on Ni(110). The angular distribution of metastable desorption is strongly peaked in the normal direction, as is also found for ionic desorption products. This indicates that the metastable is repelled along the direction of the bond being broken. We also observe an asymmetry in the azimuthal angular distribution which is correlated with the substrate crystal structure. The metastable exhibits a maximum in its yield versus coverage.

Neutron scattering has shown that the lowest spin excitations in the spin-1 antiferromagnet ${\mathrm{CsNiCl}}_3$ in its one-dimensional phase occur at finite frequency. After allowance for the known weak interchain coupling the gap is found to be in good agreement with recent numerical calculations. The results support the Haldane conjecture that in integral-spin chains with isotropic interactions a gap separates the ground state from the excitations.